Patient interfaces, such as masks in pressure support systems, are used for delivering gas to a user. Such gases like air, cleaned air, oxygen, or any modification thereof are submitted to the user (also referred to as patient) via the patient interface in a pressurized or unpressurized way.
For several chronic disorders and diseases the usage of such a patient interface is necessary or at least advisable.
One example of such a disease is obstructive sleep apnea or obstructive sleep apnea syndrome (OSA). OSA is usually caused by an obstruction of the upper airway. It is characterized by repetitive pauses in breathing during sleep and is usually associated with a reduction in blood oxygen saturation. These pauses in breathing, called apneas, typically last 20 to 40 seconds. The obstruction of the upper airway is usually caused by reduced muscle tonus of the body that occurs during sleep. The human airway is composed of walls of soft tissue which can collapse and thereby obstruct breathing during sleep. Tongue tissue moves towards the back of the throat during sleep and thereby blocks the air passages. OSA is therefore commonly accompanied with snoring.
Different invasive and non-invasive treatments for OSA are known. One of the most powerful non-invasive treatments is the usage of Continuous Positive Airway Pressure (CPAP) or Bi-Positive Airway Pressure (BiPAP) in which a patient interface, e.g. a face mask, is attached to a tube and a machine that blows pressurized gas, preferably air, into the patient interface and through the airway of the patient in order to keep it open. Positive air pressure is thus provided to a patient through a hose connected to a patient interface or respiratory interface, such as a face mask, that is worn by the patient regularly at night. The afore-mentioned long-term use of the patient interface is the result, since the wearing of the patient interface usually takes place during the sleeping time of the patient.
Examples for patient interfaces are:
nasal masks, which fit over the nose and deliver gas through the nasal passages,
oral masks, which fit over the mouth and deliver gas through the mouth,
full face masks, which fit over both, the nose and the mouth, and deliver gas to both, and
nasal pillows, which are regarded as masks as well within the scope of the present invention and which consist of small nasal inserts that deliver the gas directly to the nasal passages.
In order to guarantee a reliable operation of the device, the patient interface needs to closely fit on the patient's face to provide an air-tight seal at the mask-to-face interface. Usually, the patient interface is worn using a head gear with straps that go around the back of the patient's head. The patient interface or mask in practice usually comprises a soft cushion that is used as mask-to-patient interface, i.e. that contacts the face of the patient when the mask is worn, as well as it usually comprises a so-called mask shell building a rigid or semi-rigid holding structure for holding the cushion in place and for supplying mechanical stability to the patient interface.
The cushion usually comprises one or more pads made of gel or silicone or any other soft material in order to increase the patient comfort and guarantee a soft feeling on the patient's face. The latter-mentioned mask shell usually also comprises a hose interface that is adapted for connecting the air supplying hose to the mask. Depending on the type of the mask, it may also comprise a mechanism with an additional cushion support on the forehead to balance the forces put by the mask around the airway entry features of the human face.
Since the above-mentioned patient interfaces are usually worn over night and on a long-term basis, it is evident that e.g. cleaning of the patient interface is, especially for hygienic reasons, of great importance. It is therefore desirable that the patient interface may be disassembled into different parts in order to ease the cleaning of the patient interface. In addition, parts of the patient interface, such as cushions, have to be replaced frequently as they can wear out as a consequence of material degradation over time. These parts of the patient interface which are in immediate contact with the skin may contain compounds having a predefined functionality such as compounds assisting in avoiding skin infection or skin irritations, in particular redness, or skin damage/breakdown due to regular long-term usage of the patient interface. Examples of these compounds comprise moisture uptake means and anti microbial agents. These compounds are however subjected to loss and/or decomposition with the consequence that the mask or parts thereof require substitution.
In the art difficulties relating to the question when a device or parts thereof need replacement due to wear have been addressed to by providing devices providing an indication that after a predefined time limit replacement of the device is required.
US 2009/0199857 A1 informs about such a mask including a patient interface and a reminder system provided to the patient interface. The reminders may be based on chemicals and changes in appearance on parts of the mask itself. Chemicals may be provided indicating after a predetermined period of time that replacement is required.
U.S. Pat. No. 4,488,547 A discloses a surgical mask which changes color to signal a significant loss of bacterial filtration efficiency due to moisture accumulation. Said mask has a layer of a bacterial filtration material of a first color. A hygroscopic material partially covers a surface of said layer of filtration material and serves for the absorption of water from respired air. Absorption causes said hydroscopic material to change color to a second color not identical to said first color. Color change from said first color to said second color indicates that replacement of the mask is required.
US 2010/0018534 A1 refers to a patient interface, wherein the interface material may be made of a foam acting as heat and moisture exchanger. It is further mentioned that the foam structure may have a certain usage life or lifespan. The foam structure may include an end-of-life indicator to indicate that the end of usage life has been reached.
U.S. Pat. No. 4,155,358 pertains to a disposable valveless chemical cartridge respirator for filtration of vinyl chloride monomer. The cartridge has an end of service life indicator. The indicator system is based on potassium permanganate changing its color due to the reductive influence of vinyl chloride.
The systems of the state of the art for indicating that the replacement is required exhibit essentially the same drawbacks. Both prior art documents rely on external factors for determining span of life of the devices. Said factors however are not directly reflecting properties of the material undergoing wear out along with material functionality change, i.e., with the consequence that the remaining span of live of the devices may not be exactly ascertained, but only roughly estimated.